The Saudi-led coalition is prepared to use “calibrated force” to push the Iranian-aligned Houthi movement to withdraw from Yemen’s Hodeidah port city under a UN-sponsored deal, a senior UAE official said on Wednesday.

Yemen’s warring parties have failed to pull troops from the country’s main port under a month-old truce, reviving the threat of an all-out assault on Hodeidah that risks cutting supply lines and unleashing famine.

The Houthis control Hodeidah while other Yemeni factions backed by the coalition trying to restore the internationally recognised government are massed on its outskirts.

“Coalition prepared to use more calibrated force to prod Houthi compliance with Stockholm Agreement,” he tweeted.

“To preserve ceasefire & any hope for political process, UN and international community must press Houthis to stop violations, facilitate aid convoys, and move forward on withdrawal from Hodaida city & ports as agreed,” he added.

UN envoy Martin Griffiths has been shuttling between the parties to rescue the deal, the first major diplomatic breakthrough of the nearly four-year-old war.

The ceasefire in Hodeidah, the entry point for the bulk of Yemen’s commercial imports and aid, has largely held although sporadic skirmishes continued in flashpoints in the city. In other areas of the poorest Arabian Peninsula nation, including the Houthi-held capital Sanaa, fighting has escalated.

The warring parties disagree over who would control Hodeidah under the deal reached at December peace talks in Sweden between the Houthis and the government of Abd-Rabbu Mansour Hadi, which was ousted from power in Sanaa in late 2014.

Stalemate

Both sides have accused one another of violating the pact. A coalition source said in a statement sent to Reuters that Wednesday’s strikes were “legal” as the ceasefire only applied to Hodeidah governorate.

The war has been stalemated for years, with the alliance that intervened in 2015 unable to dislodge the Houthis, who control most urban centres. Hadi’s government controls the southern port city of Aden and a string of coastal towns.

Coalition forces led by the UAE have twice attempted to capture Hodeidah port since last year to weaken the Houthis, but had held off from a full-blown assault amid global concern over the world’s most urgent humanitarian crisis.

The war and the ensuing economic collapse has left 15.9 million people facing severe hunger.

Western nations, some of which supply the coalition with arms and intelligence, are pressing for an end to the conflict which is widely seen in the region as a proxy war between Saudi Arabia and Iran.

The Houthis deny receiving help from Iran and say their revolution is against corruption.